The fabrication of a semiconductor device involves a plurality of discrete and complex processes. The semiconductor substrate typically undergoes many processes during the fabrication process. Some of these processes may involve processing the substrate using an ion beam. For example, the substrate may be implanted with ions from the ion beam. In another embodiment, an ion beam may be used to perform an etching, amorphization or deposition process.
In certain embodiments, it may be beneficial to process the substrate while the substrate is at an elevated temperature. This may be achieved by disposing the substrate on a heated platen, which maintains the substrate at the elevated temperature. To process the substrate, the ion beam and the platen are then moved relative to one another. For example, in some embodiments, the ion beam may be a ribbon beam which extends across the diameter of the substrate. In this embodiment, the ion beam may remain stationary while the platen is translated in a direction perpendicular to the width of the ion beam. Alternatively, the substrate may remain stationary while the ion beam is translated in a direction perpendicular to its width.
However, a substrate subject to an ion implantation at an elevated temperature may be subject to three different types of temperature non-uniformity. First, there may be temporal non-uniformity, where the substrate is cooler during the initial portion of the implantation process than during the remainder of the process. This may be due to the time for the platen to elevate the temperature of the substrate. This may also be due to the fact that the ion beam imparts heat to the substrate, which is not present before implanting begins. Second, there may be spatial non-uniformity. The center of the substrate may be at a higher temperature than the outer edge of the substrate. This may be due to the fact that the outer edge of the substrate is not in contact with the platen in typical configurations. Third, there may be differences in the temperature variation. For example, the center of the substrate may remain closer to the target temperature, such as +/−7° C., while the outside of the substrate may experience temperature excursions of greater than 20° C.
Thus, it would be beneficial if there were a technique and an apparatus to reduce these sources of temperature non-uniformity that occur during the processing of substrates. Further, it would be advantageous if the apparatus were easily added to existing implantation systems. Further, it would be beneficial if the apparatus were less expensive and more reliable than existing systems.